a Estimates are as of July 1 for each year. The numbers for each sub-category in each year may not add up to the total population due to rounding.

b New metropolitan area definitions were published by the Office of Management and Budget (OMB) in 2003. These definitions were applied to population data by the Census Bureau beginning with the data from the 2000 Census. A new term, core based statistical areas (CBSAs), collectively refers to metropolitan and micropolitan statistical areas. A metropolitan statistical area is defined as having at least one urbanized area of 50,000 or more inhabitants. A micropolitan statistical area is defined as having at least one urban cluster of more than 10,000 but less than 50,000 inhabitants. All geographic boundaries for the July 1, 2009 population estimates series are defined as of January 1, 2009. The Office of Management and Budget's statistical area definitions for metropolitan and micropolitan statistical areas, as well as metropolitan divisions, are those issued by that agency in November 2008. The estimates for 2010-12 are based on the 2010 Census and reflect changes to the April 1, 2010 population due to the Count Question Resolution program and geographic program revisions. The Office of Management and Budget's statistical area delineations for metropolitan and micropolitan statistical areas, as well as metropolitan divisions, are those issued by that agency in February 2013.

c Numbers prior to 1999 are estimated to the nearest million.

d As of April 1 of year indicated. The Census Bureau only tabulates urban / rural numbers for the decennial census years.

e Fiscal year ending September 30.

f The Census Bureau calculates square mileage comprising land and water area for the decennial census years. Data for 1980 comprises land and inland water. Data for 1990 comprises land, Great Lakes, inland water, and coastal water. Data for 2000 comprises land, Great Lakes, inland water, territorial water, and coastal water.

g Sums of chained-dollar estimates for individual industries do not add to national totals because the chain-type indices used to derive them are based on weights of more than one period.

h Converted to constant 2005 dollars by the Bureau of Transportation Statistics using the CPI-U-RS price index.

1980-85: U.S. Department of Commerce, Bureau of Economic Analysis, National Economic Accounts, National Income and Product Accounts Table, table 1.1.6, available at http://www.bea.gov/national/index.htm as of Aug. 30, 2010.

U.S. Department of Labor, Bureau of Labor Statistics, Current Population Survey, Employment status of the civilian noninstitutional population, Household Date, 1 and A-2, available at http://www.bls.gov/cps/tables.htm#empstat as of Nov. 2, 2015.